The invention refers to a roller conveyor for heavy, individually packed goods units such as heavy individually packed hoods units, such as pallets
A retarding roller conveyor is already known from the European patent specifications EP 0 543 336 A1, whose carrier rollers can be stopped or, respectively, activated by sections in order to convey individually packed goods units without dynamic pressure. The goods units are moved in the conveying direction by a continuous flat belt whose upper strand--in order to transfer the drive forces--can be lifted up towards the carrier rollers by means of hugger rollers. Each hugger roller rests on the end of a double lever that can be rotated around a horizontally oriented axis that is arranged at right angles to the conveying direction. Viewed in the conveying direction, the hugger rollers are arranged in every second space present between the consecutive and spaced carrier rollers. The hugger's upward (lift) movement lifts the flat belt against the carrier roller. The transfer of the drive forces is effected by swinging the double lever horizontally via a pneumatic cylinder that engages it. This lifts the hugger rollers to the extent that the flat belt is slightly and unilaterally wrapped around the carrier rollers. The pneumatic cylinders of each hugger roller section are interconnected via a controlling device, so that all hugger rollers in the same section can be lifted or lowered jointly.
Carrier rollers are braked by braking elements, arranged in pairs at the end of the double lever facing the hugger roller, mounted in such a way that the two carrier rollers next to the double lever can be braked jointly. For this purpose, the braking elements are pressed upwards against the carrier rollers. Since the hugger roller and the two braking elements are arranged at the opposing ends of the shared double lever, the carrier rollers 25 depending on the swing position of the double lever--are either activated or braked.
This type of sectional drive operation for accumulator roller conveyors may cause problems when very heavy goods units are to be conveyed within a short period of time, or when additionally and at the same time several sections of the retarding roller conveyor are to be activated during a so-called block retraction. This may cause the drive belt to stretch and to slip between the flat belt and the carrier rollers and may reduce the wrap-around angle between the carrier roller and the flat belt, all of which may retard the speed-up and, thus, lead to a non-repeatable/reproduceable speed-up behavior of the retarding roller conveyor. In order to prevent possible goods units collisions that this may cause, safeguards in the form of lengthened retarding site sections have to be provided. This will also prevent the drive belt to suffer higher wear if it should slip.
A similarly executed retarding roller conveyor is known from the U.S. Pat. No. 3,420,356. Here as well, the carrier rollers are impelled via a driven flat belt that can be lifted towards them. The lifting of the flat belt is effected via the hugger rollers that are arranged below the respective carrier rollers. The hugger rollers themselves are permanently fixed and, therefore, not adjustable vertically, and their periphery is provided with a flattened area. When this flattened area faces the carrier rollers, the flat belt slides over it, but without activating the carrier rollers. By turning the hugger rollers' non-flattened part towards the carrier roller, the flat belt is lifted so as to come into contact with the lower part of the carrier roller and thus activating it. Due to the hugger roller's special peripheral shape, the carrier rollers--depending on the direction in which the hugger roller turns--are alternately impelled or not. If now, during the retarding stage, some part of the conveyed goods is stopped on the carrier rollers from the outside; then, in order to prevent any further drive force transfers from the flat belt to the carrier roller, a specially designed hugger roller is being provided that has a laterally arranged, additional drive pulley; the pulley's diameter is selected in such a way that it will assure constant contact with the carrier roller. When retarding of a part of the conveyed goods occurs, the pulley curbs both the carrier roller's and the hugger roller's rotational movement somewhat, while keeping the drive rollers rotating sufficiently to detach the flat belt form the lower surface of the carrier; however, the pulley inhibits any rotation that would lift the flat belt up to the lower surface of the carrier roller, as long as the part of the goods being conveyed that rests on the carrier roller is impending the bugger roller's rotation.